Can't open Firefox. When I try to open, a window pops saying "Close Firefox" and "A copy of Firefox is already open. Only one copy of Firefox can be open at a time.", and doesn't allow the application to open.

Came home to find computer restarted, which I assume is an automatic Firefox update.
When I try to open Firefox, window pops up saying "Close Firefox" and, "A copy of Firefox is already open. Only one copy of Firefox can be open at a time."
I'm unable to open the program at this time, lots of critical work info stored there - please help. Thx.
Neal

See "Hang at exit":
*http://kb.mozillazine.org/Firefox_hangs
*https://support.mozilla.com/kb/Firefox+hangs

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When I click on the icon to open Firefox I get an error message " A copy of Firefox is already open, only one copy of Firefox can be open at a time".

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Can't open Firefox. When I try to open, a window pops saying "Close Firefox" and "A copy of Firefox is already open. Only one copy of Firefox can be open at a time.", and doesn't allow the application to open.

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